Auto-focus apparatuses for recent video cameras prevalently adopt a system which attains focus adjustment by detecting sharpness of a frame from a video signal obtained by photoelectrically converting an object image by an image sensing element or the like so as to obtain an AF (auto focus) evaluation value, and controlling a focus lens position so as to maximize the AF evaluation value.
As the AF evaluation value, a high-frequency component level of a video signal, which is extracted by a bandpass filter of a given frequency band, is generally used. That is, when a normal object image is sensed, the high-frequency component level increases as the focus lens position approaches an in-focus position. Hence, a point corresponding to the maximum high-frequency component level is determined as an in-focus position.
An actual video camera that can sense a still image executes AF control as follows. That is, the focus lens is controlled to smoothly maintain an in-focus position during monitoring before sensing a still image. When the user has pressed the release switch to sense a still image, the focus lens is controlled to quickly move to an in-focus position.
However, when the release switch for sensing a still image has half- and full-stroke positions, a blurred image may be recorded depending on the depression timing of the release switch by the user. In order to avoid such blurred image, the AF in-focus time is prolonged.